Schultz, who left the network in 2015, reportedly died of natural causes.
Former MSNBC primetime host Ed Schultz has died of natural causes at the age of 64, the network reported on air on Thursday.
Schultz joined the network in 2009. His show, The Ed Show, was canceled in 2015 as part of a wave of programmatic tinkering at the network.
"Ed was a brilliant and persistent voice for those without a voice in this country," Dylan Ratigan, Schultz's former colleague at MSNBC, told The Hollywood Reporter.
The pugnacious Schultz began hosting a show for Russian government-sponsored RT America in early 2016.
Schultz, who began as a conservative and became a prominent liberal, was a longtime, highly rated radio host.
"Ed Schultz was incredibly kind to me when I was first doing TV on MSNBC," The Daily Beast's Sam Stein wrote on Twitter. "He had a complex personality but was also remarkably generous."
"RIP, Ed. You had a large heart and a loud voice," wrote Mother Jones reporter David Corn.
Schultz was an early critic of President Trump but complimented him for campaigning on improvements to trade and manufacturing.